Channel selection in power line communications

ABSTRACT

A power line communication (PLC) device comprises a processor and a memory coupled to the processor. The memory is configured to store program instructions executable by the processor to cause the PLC device perform operations. One or more time slots are sequentially scan in each of a plurality of frequency bands. A packet transmitted by a second PLC device to the PLC device over one of the plurality of frequency bands is detected. Additional packets received from the second PLC device across the plurality of frequency bands based, at least in part, upon the detected packet are synchronized. The additional packets are organized in a plurality of frames, each of the plurality of frames having been transmitted by the second PLC device to the PLC device over a respective one of the plurality of frequency bands. Each frame has a plurality of time slots, and each time slot has a pair of beacon and bandscan packets, Each bandscan packet includes information indicating a frequency band distinct from any of the plurality of different frequency bands to be used by the second PLC device to communicate with the first PLC device in a direction from the second PLC device to the first PLC device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of and claims priority to U.S. patentapplication Ser. No. 13/363,391 filed Feb. 1, 2012. Said applicationclaims the benefit of the filing date of U.S. Provisional PatentApplication No. 61/440,576 titled “Automatic Channel Scan Algorithm” andfiled Feb. 8, 2011. Said applications are hereby incorporated byreference herein in its entirety.

TECHNICAL FIELD

This specification is directed, in general, to power linecommunications, and, more specifically, to systems and methods ofchannel selection in power line communications.

BACKGROUND

Power line communications (PLC) include systems for communicating dataover the same medium (i.e., a wire or conductor) that is also used totransmit electric power to residences, buildings, and other premises.Once deployed, PLC systems may enable a wide array of applications,including, for example, automatic meter reading and load control (i.e.,utility-type applications), automotive uses (e.g., charging electriccars), home automation (e.g., controlling appliances, lights, etc.),and/or computer networking (e.g., Internet access), to name only a few.

Various PLC standardizing efforts are currently being undertaken aroundthe world, each with its own unique characteristics. Generally speaking,PLC systems may be implemented differently depending upon localregulations, characteristics of local power grids, etc. Examples ofcompeting PLC standards include the IEEE 1901, HomePlug AV, and ITU-TG.hn (e.g., G.9960 and G.9961) specifications. Another standardizationeffort includes, for example, the Powerline-Related Intelligent MeteringEvolution (PRIME) standard designed for OFDM-based (OrthogonalFrequency-Division Multiplexing) communications.

SUMMARY

Systems and methods for channel selection in power line communications(PLC) are described. In an illustrative, non-limiting embodiment, amethod may include performing, by a first PLC device, defining aplurality of frames, each of the plurality of frames having a pluralityof time slots. The method may also include performing, by the first PLCdevice, assembling a pair of beacon and bandscan packets within each ofthe plurality of time slots in each of the plurality of frames. Themethod may further include performing, by the first PLC device,sequentially transmitting each of the plurality of frames in acorresponding one of a plurality of different frequency bands to asecond PLC device over a power line.

For example, the first PLC device may include a PLC modem. The beaconpackets may be configured to inform the second PLC device that the firstPLC device is active. Each bandscan packet may include a slot indexindicating a position of its time slot within its respective frame. Eachbandscan packet may also include a band index indicating one of theplurality of different frequency bands. In addition, each bandscanpacket may include information indicating a frequency band distinct fromany of the plurality of different frequency bands to be used by thesecond PLC device to communicate with the first PLC device in adirection from the second PLC device to the first PLC device. In somecases, the information may include signal-to-noise ratio (SNR) and/orbit error rate (BER) information.

In some implementations, the method may include performing, by the firstPLC device and in response to having transmitted the plurality offrames, receiving one or more packets from the second PLC deviceindicating a selection of one or more of the plurality of differentfrequency bands to be used in a communication between the first PLCdevice and the second PLC device in a direction from the first PLCdevice to the second PLC device. In other implementations, the methodmay also include performing, by the first PLC device and in response tohaving transmitted the plurality of frames, receiving one or morepackets from the second PLC device indicating a signal-to-noise ratio(SNR) or bit error rate (BER) measurement made by the second PLC devicein each of the plurality of different frequency bands. In the lattercase, the method may further include selecting one or more of theplurality of different frequency bands to be used in a communicationbetween the first PLC device and the second PLC device in a directionfrom the first PLC device to the second PLC device based, at least inpart, upon the SNR or BER measurements.

In another illustrative, non-limiting embodiment, a method may includeperforming, by a PLC device, sequentially scanning one or more timeslots in each of a plurality of frequency bands, detecting a packettransmitted by a second PLC device to the PLC device over one of theplurality of frequency bands, and synchronizing additional packetsreceived from the second PLC device across the plurality of frequencybands based, at least in part, upon the detected packet, wherein theadditional packets are organized in a plurality of frames, each of theplurality of frames having been transmitted by the second PLC device tothe PLC device over a respective one of the plurality of frequencybands, each frame having a plurality of time slots, and each time slothaving a pair of beacon and bandscan packets.

For example, the beacon packets may be configured to inform the PLCdevice that the second PLC device is active. In addition, each bandscanpacket may include a slot index indicating a position of its time slotwithin its respective frame and/or a band index indicating acorresponding one of the plurality of frequency bands. The method mayalso include calculating a channel quality metric for each of theplurality of frequency bands based, at least in part, upon respectiveones of the plurality of frames. For instance, the channel qualitymetric may include a signal-to-noise ratio (SNR) or bit error rate (BER)calculation or estimation.

In some implementations, the method may include transmitting one or morepackets to the second PLC device, each of the one or more packetscorresponding to one of the plurality of time slots, and each of one ormore packets including an indication of the channel quality metric. Inthat regard, the method may include determining when to transmit the oneor more packets to the second PLC device based upon at least one of: around-robin or a carrier sense multiple access (CSMA) technique.

In yet another illustrative, non-limiting embodiment, a method mayinclude performing, by a first PLC modem and in a first mode ofoperation, defining a plurality of frames, each of the plurality offrames having a plurality of time slots, assembling a pair of beacon andbandscan packets within each of the plurality of time slots in each ofthe plurality of frames, and sequentially transmitting each of theplurality of frames over a corresponding one of a first plurality offrequency bands to a second PLC modem over a power line. In a secondmode of operation, the method may include performing, by the first PLCmodem, monitoring one or more time slots in each of a second pluralityof frequency bands over the power line, the second plurality offrequency bands different from the first plurality of frequency bands,detecting a packet transmitted by the second PLC modem over one of thesecond plurality of frequency bands, synchronizing receipt of additionalpackets transmitted by the second PLC modem across the second pluralityof frequency bands based, at least in part, upon the detected packet,calculating a channel quality value for each of the second plurality offrequency bands based, at least in part, upon the additional packets,and selecting one or more of the second plurality of frequency bands forsubsequent communications with the second PLC modem in a direction fromthe second PLC modem to the first PLC modem based, at least in part,upon the channel quality values.

In the first mode of operation, the method may also include receiving acommunication from the second PLC modem indicating one or more of thefirst plurality of frequency bands to be used in subsequentcommunications with the second PLC modem in a direction from the firstPLC modem to the second PLC modem. In the second mode of operation, themethod may further include communicating the selected one or more of thesecond plurality of frequency bands to the second PLC modem over each ofthe second plurality of frequency bands, the selected one or more of thesecond plurality of frequency bands to be used in subsequentcommunications with the PLC modem in a direction from the second PLCmodem to the first PLC modem.

In some implementations, one or more PLC devices or computer systems mayperform one or more of the techniques described herein. In otherimplementations, a tangible computer-readable or electronic storagemedium may have program instructions stored thereon that, upon executionby one or more PLC devices or computer systems, cause the one or morePLC devices or computer systems to execute one or more operationsdisclosed herein. In yet other implementations, a PLC system (e.g., aPLC modem) may include at least one processor and a memory coupled tothe at least one processor. Examples of a processor include, but are notlimited to, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a system-on-chip (SoC) circuit, afield-programmable gate array (FPGA), a microprocessor, or amicrocontroller. The memory may be configured to store programinstructions executable by the at least one processor to cause thesystem to execute one or more operations disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention(s) in general terms, reference willnow be made to the accompanying drawings, wherein:

FIG. 1 is a block diagram of a power line communication (PLC)environment according to some embodiments.

FIG. 2 is a block diagram of a PLC device or modem according to someembodiments.

FIG. 3 is a block diagram of an integrated circuit according to someembodiments.

FIGS. 4-6 are block diagrams illustrating connections between a PLCtransmitter and/or receiver circuitry to three-phase power linesaccording to some embodiments.

FIG. 7 is a flowchart of a method for creating a superframe according tosome embodiments.

FIG. 8 is a diagram of a superframe according to some embodiments.

FIG. 9 is a flowchart of a passive listening method according to someembodiments.

FIG. 10 is a diagram of a single PLC device in passive listening modeaccording to some embodiments.

FIG. 11 is a diagram of multiple PLC devices operating in passivelistening mode according to some embodiments.

FIG. 12 is a flowchart of an active listening method according to someembodiments.

FIG. 13 is a diagram of a single PLC device in active listening modeaccording to some embodiments.

FIG. 14 is a diagram of multiple PLC devices operating in activelistening mode according to some embodiments.

FIG. 15 is a block diagram of a computing system configured to implementcertain systems and methods described herein according to someembodiments.

DETAILED DESCRIPTION

The invention(s) now will be described more fully hereinafter withreference to the accompanying drawings. The invention(s) may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention(s) to a person of ordinaryskill in the art. A person of ordinary skill in the art may be able touse the various embodiments of the invention(s).

Turning to FIG. 1, an electric power distribution system is depictedaccording to some embodiments. Medium voltage (MV) power lines 103 fromsubstation 101 typically carry voltage in the tens of kilovolts range.Transformer 104 steps the MV power down to low voltage (LV) power on LVlines 105, carrying voltage in the range of 100-240 VAC. Transformer 104is typically designed to operate at very low frequencies in the range of50-60 Hz. Transformer 104 does not typically allow high frequencies,such as signals greater than 100 KHz, to pass between LV lines 105 andMV lines 103. LV lines 105 feed power to customers via meters 106 a-n,which are typically mounted on the outside of residences 102 a-n.(Although referred to as “residences,” premises 102 a-n may include anytype of building, facility or location where electric power is receivedand/or consumed.) A breaker panel, such as panel 107, provides aninterface between meter 106 n and electrical wires 108 within residence102 n. Electrical wires 108 deliver power to outlets 110, switches 111and other electric devices within residence 102 n.

The power line topology illustrated in FIG. 1 may be used to deliverhigh-speed communications to residences 102 a-n. In someimplementations, power line communications modems or gateways 112 a-nmay be coupled to LV power lines 105 at meter 106 a-n. PLCmodems/gateways 112 a-n may be used to transmit and receive data signalsover MV/LV lines 103/105. Such data signals may be used to supportmetering and power delivery applications (e.g., smart gridapplications), communication systems, high speed Internet, telephony,video conferencing, and video delivery, to name a few. By transportingtelecommunications and/or data signals over a power transmissionnetwork, there is no need to install new cabling to each subscriber 102a-n. Thus, by using existing electricity distribution systems to carrydata signals, significant cost savings are possible.

An illustrative method for transmitting data over power lines may use,for example, a carrier signal having a frequency different from that ofthe power signal. The carrier signal may be modulated by the data, forexample, using an orthogonal frequency division multiplexing (OFDM)scheme or the like.

PLC modems or gateways 112 a-n at residences 102 a-n use the MV/LV powergrid to carry data signals to and from PLC data concentrator 114 withoutrequiring additional wiring. Concentrator 114 may be coupled to eitherMV line 103 or LV line 105. Modems or gateways 112 a-n may supportapplications such as high-speed broadband Internet links, narrowbandcontrol applications, low bandwidth data collection applications, or thelike. In a home environment, for example, modems or gateways 112 a-n mayfurther enable home and building automation in heat and airconditioning, lighting, and security. Also, PLC modems or gateways 112a-n may enable AC or DC charging of electric vehicles and otherappliances. An example of an AC or DC charger is illustrated as PLCdevice 113. Outside the premises, power line communication networks mayprovide street lighting control and remote power meter data collection.

One or more data concentrators 114 may be coupled to control center 130(e.g., a utility company) via network 120. Network 120 may include, forexample, an IP-based network, the Internet, a cellular network, a WiFinetwork, a WiMax network, or the like. As such, control center 130 maybe configured to collect power consumption and other types of relevantinformation from gateway(s) 112 and/or device(s) 113 throughconcentrator(s) 114. Additionally or alternatively, control center 130may be configured to implement smart grid policies and other regulatoryor commercial rules by communicating such rules to each gateway(s) 112and/or device(s) 113 through concentrator(s) 114.

In some embodiments, each concentrator 114 may be seen as a base nodefor a PLC domain, each such domain comprising downstream PLC devicesthat communicate with control center 130 through a respectiveconcentrator 114. For example, in FIG. 1, device 106 a-n, 112 a-n, and113 may all be considered part of the PLC domain that has dataconcentrator 114 as its base node; although in other scenarios otherdevices may be used as the base node of a PLC domain. In a typicalsituation, multiple nodes may be deployed in a given PLC network, and atleast a subset of those nodes may be tied to a common clock through abackbone (e.g., Ethernet, digital subscriber loop (DSL), etc.).

Still referring to FIG. 1, meter 106, gateways 112, PLC device 113, anddata concentrator 114 may each be coupled to or otherwise include a PLCmodem or the like. The PLC modem may include transmitter and/or receivercircuitry to facilitate the device's connection to power lines 103, 105,and/or 108.

FIG. 2 is a block diagram of PLC device or modem 113 according to someembodiments. As illustrated, AC interface 201 may be coupled toelectrical wires 108 a and 108 b inside of premises 112 n in a mannerthat allows PLC device 113 to switch the connection between wires 108 aand 108 b off using a switching circuit or the like. In otherembodiments, however, AC interface 201 may be connected to a single wire108 (i.e., without breaking wire 108 into wires 108 a and 108 b) andwithout providing such switching capabilities. In operation, ACinterface 201 may allow PLC engine 202 to receive and transmit PLCsignals over wires 108 a-b. As noted above, in some cases, PLC device113 may be a PLC modem. Additionally or alternatively, PLC device 113may be a part of a smart grid device (e.g., an AC or DC charger, ameter, etc.), an appliance, or a control module for other electricalelements located inside or outside of premises 112 n (e.g., streetlighting, etc.).

PLC engine 202 may be configured to transmit and/or receive PLC signalsover wires 108 a and/or 108 b via AC interface 201 using a particularchannel or frequency band. In some embodiments, PLC engine 202 may beconfigured to transmit OFDM signals, although other types of modulationschemes may be used. As such, PLC engine 202 may include or otherwise beconfigured to communicate with metrology or monitoring circuits (notshown) that are in turn configured to measure power consumptioncharacteristics of certain devices or appliances via wires 108, 108 a,and/or 108 b. PLC engine 202 may receive such power consumptioninformation, encode it as one or more PLC signals, and transmit it overwires 108, 108 a, and/or 108 b to higher-level PLC devices (e.g., PLCgateways 112 n, data concentrators 114, etc.) for further processing.Conversely, PLC engine 202 may receive instructions and/or otherinformation from such higher-level PLC devices encoded in PLC signals,for example, to allow PLC engine 202 to select a particular frequencyband in which to operate.

In various embodiments, PLC device 113 may be implemented at least inpart as an integrated circuit. FIG. 3 is a block diagram of such anintegrated circuit. In some cases, one or more of meter 106, gateway112, PLC device 113, or data concentrator 114 may be implementedsimilarly as shown in FIG. 3. For example, integrated circuit 302 may bea digital signal processor (DSP), an application specific integratedcircuit (ASIC), a system-on-chip (SoC) circuit, a field-programmablegate array (FPGA), a microprocessor, a microcontroller, or the like. Assuch, integrated circuit 302 may implement, at least in part, at least aportion of PLC engine 202 shown in FIG. 2. Integrated circuit 302 iscoupled to one or more peripherals 304 and external memory 303. Further,integrated circuit 302 may include a driver for communicating signals toexternal memory 303 and another driver for communicating signals toperipherals 304. Power supply 301 is also provided which supplies thesupply voltages to integrated circuit 302 as well as one or more supplyvoltages to memory 303 and/or peripherals 304. In some embodiments, morethan one instance of integrated circuit 302 may be included (and morethan one external memory 303 may be included as well).

Peripherals 304 may include any desired circuitry, depending on the typeof PLC device or system. For example, in some embodiments, peripherals304 may implement, at least in part, at least a portion of a PLC modem(e.g., portions of AC interface 210 shown in FIG. 2). Peripherals 304may also include additional storage, including RAM storage, solid-statestorage, or disk storage. In some cases, peripherals 304 may includeuser interface devices such as a display screen, including touch displayscreens or multi-touch display screens, keyboard or other input devices,microphones, speakers, etc. External memory 303 may include any type ofmemory. For example, external memory 303 may include SRAM, nonvolatileRAM (NVRAM, such as “flash” memory), and/or dynamic RAM (DRAM) such assynchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.)SDRAM, etc. External memory 303 may include one or more memory modulesto which the memory devices are mounted, such as single inline memorymodules (SIMMs), dual inline memory modules (DIMMs), etc.

In various implementations, PLC device or modem 113 may includetransmitter and/or receiver circuits configured to connect to powerlines 103, 105, and/or 108. FIG. 4 illustrates the connection betweenthe power line communication transmitter and/or receiver circuitry tothe power lines according to some embodiments. PLC transmitter/receiver401 may function as the transmitter and/or receiver circuit. PLCtransmitter/receiver 401 generates pre-coded signals for transmissionover the power line network. Each output signal, which may be a digitalsignal, is provided to a separate line driver circuit 402A-C. Linedrivers 402A-C comprise, for example, digital-to-analog conversioncircuitry, filters, and/or line drivers that couple signals from PLCtransmitter/receiver 401 to power lines 403A-C. Transformer 404 andcoupling capacitor 405 link each analog circuit/line driver 402 to itsrespective power line 403A-C. Accordingly, in the embodiment illustratedin FIG. 4, each output signal is independently linked to a separate,dedicated power line.

FIG. 4 further illustrates an alternate receiver embodiment. Signals arereceived on power lines 403A-C, respectively. In an embodiment, each ofthese signals may be individually received through coupling capacitors405, transformers 404, and line drivers 402 to PLC transmitter/receiver401 for detection and receiver processing of each signal separately.Alternatively, the received signals may be routed to summing filter 406,which combines all of the received signals into one signal that isrouted to PLC transmitter/receiver 401 for receiver processing.

FIG. 5 illustrates an alternative embodiment in which PLCtransmitter/receiver 501 is coupled to a single line driver 502, whichis in turn coupled to power lines 503A-C by a single transformer 504.All of the output signals are sent through line driver 502 andtransformer 504. Switch 506 selects which power line 503A-C receives aparticular output signal. Switch 506 may be controlled by PLCtransmitter/receiver 501. Alternatively, switch 506 may determine whichpower line 503A-C should receive a particular signal based uponinformation, such as a header or other data, in the output signal.Switch 506 links line driver 502 and transformer 504 to the selectedpower line 503A-C and associated coupling capacitor 505. Switch 506 alsomay control how received signals are routed to PLC transmitter/receiver501.

FIG. 6 is similar to FIG. 5 in which PLC transmitter/receiver 1901 iscoupled to a single line driver 1902. However, in the embodiment of FIG.6, power lines 603A-C are each coupled to a separate transformer 604 andcoupling capacitor 605. Line driver 602 is coupled to the transformers604 for each power line 603 via switch 606. Switch 606 selects whichtransformer 604, coupling capacitor 605, and power line 603A-C receivesa particular signal. Switch 606 may be controlled by PLCtransmitter/receiver 601, or switch 606 may determine which power line603A-C should receive a particular signal based upon information, suchas a header or other data, in each signal. Switch 606 also may controlhow received signals are routed to PLC transmitter/receiver 601.

In some embodiments, the systems described above (and/or the computersystem shown in FIG. 15) may be configured to select and/or facilitatethe selection of one or more channels or frequency bands of operation.Generally speaking, a PLC device in a PLC network may be configured totransmit signals (i.e., uplink) in one or more bands of a first set offrequency bands or subbands. The same PLC device may be configured toreceive signals (i.e., downlink) in one or more bands of a second set offrequency bands or subbands. In some implementations, the first set offrequency bands may be at least in part distinct with respect to thesecond set of frequency bands. In other implementations, the first setof frequency bands may be completely non-overlapping with respect to thesecond set. Furthermore, during operation, a given PLC device may beconfigured to monitor conditions in the frequency band (or set of bands)currently in use, and, upon detecting a worsening or degradation ofthose conditions, the PLC device may automatically switch itstransmission and/or reception to a more suitable frequency band (or setof bands).

In various embodiments, in order to select or facilitate the selectionof frequency bands, two or more PLC devices may communicate with eachother to exchange information sufficient to calculate or estimatechannel conditions in the uplink and/or downlink directions. Forexample, first and second PLC devices may take turns acting as“initiator” and “listener.” In a first mode of operation, the first PLCdevice may act as initiator and may be configured to create and transmit“superframes” over a power line, as described below with respect toFIGS. 7 and 8. Upon receipt of at least a portion of a superframe, thesecond PLC device (configured to act as a listener) may measure orestimate the channel conditions in each band, and select appropriatefrequency band(s) and/or indicate the selection, for example, to a humanoperator (referred to as “passive listening” and described in FIGS.9-11). Additionally or alternatively, the second PLC device may transmitan indication of the channel conditions and/or an indication of theselected frequency band(s) to the first PLC device (referred to as“active listening” as described in FIGS. 12-14). As such, the firstand/or second PLC devices select the appropriate frequency band(s) tocommunicate in the direction from the first PLC device to the second PLCdevice. Then, in second mode of operation, the first PLC device and thesecond PLC device may switch roles and repeat the same or a similarprocess in the reverse direction. Accordingly, the first and/or secondPLC devices may also identify a suitable frequency band(s) forsubsequent communications in the direction from the second PLC device tothe first PLC device. As previously noted, the channel selection processmay be repeated periodically and/or in response to a change in channelconditions.

Turning now to FIGS. 7 and 8, a method for creating a superframe isdepicted. In some embodiments, method 700 may be performed by a computersystem, PLC device, PLC modem, or the like. At block 705, method 700 maydefine a time slot. The length of such a slot is configurable, and maybe longer than the length of a beacon packet (a packet configured toinform a PLC device that another PLC device is active). At block 710,method 700 may define a plurality of frames, each of the frames having aplurality of time slots. For instance, in the example shown in FIG. 8,frames 0-n each have p slots, where n and p are integers. At block 715,method 700 may create a plurality of bandscan packets. In someimplementations, each bandscan packet may include a band index and aslot index. Specifically, the slot index may indicate a position of atime slot within a respective frame and the band index may indicate oneof the plurality of different frequency bands with which the frame isassociated, as discussed below.

At block 720, method 700 may insert a beacon packet and a bandscanpacket in each time slot of each frame. For example, a bandscan packetinserted in the third time slot of the second frame may have a slotindex of 3 and a band index of 2, whereas another bandscan packetinserted in the sixth time slot of the fourth frame may have a slotindex of 6 and a frame index of 4. At block 725, method 700 mayassociate each frame with a given frequency band or channel, and atblock 730 these various frames 0-n may be assembled into bandscansuperframe 800, as shown in FIG. 8.

In a first mode of operation, an initiator (e.g., a transmitting PLCdevice) may create a superframe, for example, as outlined in FIG. 7, andmay transmit the superframe over a power line. In some cases, the wholesuperframe may be repeated a predetermined number of times to allow alistener (e.g., a receiving PLC device) to develop a complete channelquality report for the frequency bands (in the direction from theinitiator to the listener). Although each time slot is described asincluding two packets (i.e., a beacon packet and a bandscan packet), insome cases these two packets may be combined into one or split intothree or more packets. Moreover, in addition to slot and frame indexinformation, each bandscan packet may also include other data such as,for example, an identification of the transmitting device, channelquality information (e.g., in the direction from the listener to theinitiator—for example, generated in previous determinations, etc.).

FIG. 9 is a flowchart of a passive listening method. In someembodiments, method 900 may be performed by a computer system, PLCdevice, PLC modem, or the like. At block 905, method 900 may beginlistening for beacon packets or the like received in a selectedfrequency band or channel. At block 910, method 900 may determinewhether a beacon packet has been received in the selected frequencyband. If not, control returns to block 905 and method 900 may listen forbeacon packets in a subsequent channel frequency band. In someembodiments, block 905 may cause the PLC device to listen in theselected frequency band for a length of time equal to a time slot.Alternatively, the PLC device may listen in the same frequency band fora length of time longer than a time slot (e.g., slightly longer than atime slot, twice the length of a time slot, three times the length ofthe time slot, etc.).

If method 900 detects a beacon packet at block 910, then it may use thearrival time of the beacon packet (plus known information about thelength of the packet) to synchronize the receipt of packets inadditional or subsequent time slots. This implementation may beparticularly useful, for example, in situations where the listener andthe initiator do not have synchronized clocks. In cases where theirclocks are synchronized, however, block 915 may be optional. At block920, method 900 may identify the band to which the received packet(s)belong. In some implementations, the band may be known and equal to theband scanned in block 905. In other situations, the identity of the bandmay be extracted from received packet(s) (e.g., the band index of agiven bandscan packet).

At block 925, method 900 may include calculating or estimating a channelmetric. For example, the listener device may calculate or estimate thesignal-to-noise ratio (SNR) and/or bit error rate (BER) of the channelby comparing received packet(s) in that channel to expected packets(i.e., in the absence of noise and/or other impairments). At block 930,method 900 may determine whether the selected frequency band is the lastto be evaluated. If not, control returns to block 905 and a subsequentchannel or frequency band may be evaluated. Otherwise, method 900 mayindicate the results at block 935.

In some embodiments, the results of block 935 may include the channelmetric for each channel or frequency band. Additionally oralternatively, the results may identify frequency bands ranked from bestto worst in terms of channel metric (e.g., highest to lowest SNR, lowestto highest BER, etc.). Moreover, in some cases, the listener device maybe configured to utilize two or more frequency bands simultaneously, andthe results of block 935 may therefore identify a set of bands to beused in subsequent communications.

As a hypothetical example, assume that there are 4 possible frequencybands (i.e., n=4) and that the listener device, upon receiving one ormore superframes from the initiator device, has calculated or estimatedthe following channel metrics for each band: SNR_(BAND1)=2.0 dB,SNR_(BAND2)=3.0 dB, SNR_(BAND3)=4.0 dB, and SNR_(BAND4)=6.0 dB. In thiscase, if the bandwidth of band 4 is sufficient to enable communicationsbetween the initiator and the listener, then the results of block 935may select band 4 because it has the best channel metric (in this case,the highest SNR). If, however, the bandwidth of band 4 is not sufficientto enable communications, then bands 4 and 3 may be selected. Moregenerally, the number of channels or bands selected as a result ofmethod 900 may depend upon the bandwidth required by the listener and/ortransmitting device, which in turn may depend upon the type of deviceand/or protocol or standard being used.

In some implementations, once results are determined and/or gathered inblock 935, those results may be communicated to a human operator. Thehuman operator may then manually coordinate (e.g., with another humanoperator) the operation of the initiator device so that, in subsequentcommunications with the listener device, the initiator device may beconfigured to use the channel(s) or band(s) indicated in block 935(i.e., in the direction from the initiator device to the listenerdevice). In other embodiments, the results of block 935 may becommunicated via the power line back to the initiator device; thusavoiding human interaction. For example, the listener device maytransmit a ranked list of channels to the initiator, and the initiatormay locally execute a band selection algorithm similar or identical tothe algorithm performed by the listener device in processing the rankedlist. Additionally or alternatively, the listener device may transmitits channel or band selection to the initiator directly.

FIG. 10 is a diagram of a single PLC device in passive listening modeaccording to some embodiments. In this case, the initiator transmits abandscan superframe with frames 0-n, each frame having 0-p time slots.Meanwhile, a listener device scans each band 0-n for the duration of atime slot. In this example, assume that band 0 is not usable due tohighly degraded signal conditions. Hence, although the initiator istransmitting frame 0 over frequency band 0 at the same time when thelistener scans band 0 at time slot 1005, frame 0 is nonetheless notdetectable by the listener.

After transmitting frame 0 over band 0, however, the initiator beginstransmitting frame 1 over band 1 while the listener continues tosequentially scan each channel or band. Also assume, in this example,that band 1 is usable. Thus, at time slot 1010, the listener scans band1 (while the initiator is still transmitting frame 1 over band 1) andtherefore detects one or more packets “p-1” (e.g., a beacon packet).Upon detecting the first beacon packet, the listener may then determine,based at least in part upon the length of each time slot, the beginningof the subsequent time slot “p” 1015, thus synchronizing the receptionof additional or subsequent packets. Moreover, based on the time slotindex of the first received bandscan packet, the listener can determinewhen to switch to the subsequent channel, thus also synchronizingsubsequent band selection. In cases where the listener cannot detect abeacon packet after scanning bands for a duration equal to or greaterthan that of a superframe, that may suggest that none of the bands issuitable for use from the initiator to the listener.

FIG. 11 is a diagram of multiple PLC devices operating in passivelistening mode according to some embodiments. Scenario 1100 is similarto scenario 1000 described in FIG. 10, but with two listener devices Aand B operating concurrently on the same power line (any number oflistening devices may be used). In this case, both listeners A and Bmiss frame 0 at time slots 1105A and B, respectively. However, listenerB detects a first beacon packet during transmission of frame 0 and syncssubsequent packets at 1110B. Listener A detects a beacon packet duringtransmission of frame 1, and syncs subsequent packets at 1110A.

FIG. 12 is a flowchart of an active listening mode of operationaccording to some embodiments. Particularly, blocks 1205-1225 of method1200 may be similar to blocks 1105-1125 of method 1100 in FIG. 11. Here,however, method 1200 may transmit an indication of the estimated orcalculated channel metric back to the initiator at block 1230 in theform of an “echo” packet or the like. The echo packet may be transmittedto the initiator, for example, in the same band or channel where thebeacon packet was received. In some implementations, the echo packet mayinclude a report of channel conditions in the direction from theinitiator to the listener. The initiator may also use the echo packet toestimate channel conditions in the direction from the listener to theinitiator. After the last band is scanned, the listener device mayselect one or more bands at block 1240. Moreover, after a completesuperframe duration, both the initiator and the listener nodes may havea channel condition report in the relevant direction. That is, beacon orbandscan packets may include channel metrics for the direction from thelistener to the initiator (as determined by the initiator) and echopackets may include channel metrics for the direction from the initiatorto the listener (as determined by the listener).

FIG. 13 is a diagram of a single PLC device in active listening modeaccording to some embodiments. Specifically, diagram 1300 may be similarto diagram 1000 of FIG. 10. However, every time the initiator transmitsa time slot 1305 after synchronization, the listener device transmitsone or more echo packets back to the initiator indicating a current,previous, or accumulated channel quality metric. For example, in someimplementations, the listener device may transmit the channel qualitymetric based on the current or last received packet or subset of packetsfor the present frame. In other implementations, the listener device maytransmit the channel quality metric for every channel measured up tothat point—i.e., a cumulative report. In yet other implementations, thelistener device may transmit an indication of the current channelselection (as an alternative or in addition to the quality metrics).

FIG. 14 is a diagram of multiple PLC devices operating in activelistening mode according to some embodiments. Scenario 1400 is similarto scenario 1300 described in FIG. 13, but with two listener devices Aand B operating concurrently on the same power line (any number oflistening devices may be used). In this case, both listeners A and Btransmit echo packets to the initiator device at slots 1310 and 1405containing their respective channel metric measurements and/or bandselection(s). To avoid collision between these two or moretransmissions, the time at which listeners A and B transmit theirrespective echo packets may be determined using a Round Robin algorithmor the like. Additionally or alternatively, listeners A and B may employa Carrier Sense Multiple Access (CSMA) technique or the like.

As noted above, in certain embodiments, systems and methods for channelselection may be implemented or executed by one or more PLC devicesand/or computer systems. One such computer system is illustrated in FIG.15. In various embodiments, system 1500 may be implemented as a PLCdevice, PLC modem, PLC data concentrator, server, a mainframe computersystem, a workstation, a network computer, a desktop computer, a laptop,mobile device, or the like. In different embodiments, these varioussystems may be configured to communicate with each other in any suitableway, such as, for example, via a local area network or the like.

As illustrated, system 1500 includes one or more processors 1510 coupledto a system memory 1520 via an input/output (I/O) interface 1530.Computer system 160 further includes a network interface 1540 coupled toI/O interface 1530, and one or more input/output devices 1525, such ascursor control device 1560, keyboard 1570, display(s) 1580, and/ormobile device 1590. In various embodiments, computer system 1500 may bea single-processor system including one processor 1510, or amulti-processor system including two or more processors 1510 (e.g., two,four, eight, or another suitable number). Processors 1510 may be anyprocessor capable of executing program instructions. For example, invarious embodiments, processors 1510 may be general-purpose or embeddedprocessors implementing any of a variety of instruction setarchitectures (ISAs), such as the x815, POWERPC®, ARM®, SPARC®, or MIPS®ISAs, or any other suitable ISA. In multi-processor systems, each ofprocessors 1510 may commonly, but not necessarily, implement the sameISA. Also, in some embodiments, at least one processor 1510 may be agraphics processing unit (GPU) or other dedicated graphics-renderingdevice.

System memory 1520 may be configured to store program instructionsand/or data accessible by processor 1510. In various embodiments, systemmemory 1520 may be implemented using any suitable memory technology,such as static random access memory (SRAM), synchronous dynamic RAM(SDRAM), nonvolatile/Flash-type memory, or any other type of memory. Asillustrated, program instructions and data implementing certainoperations such as, for example, those described in the figures above,may be stored within system memory 1520 as program instructions 1525 anddata storage 1535, respectively. In other embodiments, programinstructions and/or data may be received, sent or stored upon differenttypes of computer-accessible media or on similar media separate fromsystem memory 1520 or computer system 1500. Generally speaking, acomputer-accessible medium may include any tangible storage media ormemory media such as magnetic or optical media—e.g., disk or CD/DVD-ROMcoupled to computer system 1500 via I/O interface 1530. Programinstructions and data stored on a tangible computer-accessible medium innon-transitory form may further be transmitted by transmission media orsignals such as electrical, electromagnetic, or digital signals, whichmay be conveyed via a communication medium such as a network and/or awireless link, such as may be implemented via network interface 1540.

In one embodiment, I/O interface 1530 may be configured to coordinateI/O traffic between processor 1510, system memory 1520, and anyperipheral devices in the device, including network interface 1540 orother peripheral interfaces, such as input/output devices 1550. In someembodiments, I/O interface 1530 may perform any necessary protocol,timing or other data transformations to convert data signals from onecomponent (e.g., system memory 1520) into a format suitable for use byanother component (e.g., processor 1510). In some embodiments, I/Ointerface 1530 may include support for devices attached through varioustypes of peripheral buses, such as a variant of the Peripheral ComponentInterconnect (PCI) bus standard or the Universal Serial Bus (USB)standard, for example. In some embodiments, the function of I/Ointerface 1530 may be split into two or more separate components, suchas a north bridge and a south bridge, for example. In addition, in someembodiments some or all of the functionality of I/O interface 1530, suchas an interface to system memory 1520, may be incorporated directly intoprocessor 1510.

Network interface 1540 may be configured to allow data to be exchangedbetween computer system 1500 and other devices attached to a network,such as other computer systems, or between nodes of computer system1500. In various embodiments, network interface 1540 may supportcommunication via wired or wireless general data networks, such as anysuitable type of Ethernet network, for example; viatelecommunications/telephony networks such as analog voice networks ordigital fiber communications networks; via storage area networks such asFibre Channel SANs, or via any other suitable type of network and/orprotocol.

Input/output devices 1550 may, in some embodiments, include one or moredisplay terminals, keyboards, keypads, touchpads, scanning devices,voice or optical recognition devices, mobile devices, or any otherdevices suitable for entering or retrieving data by one or more computersystem 1500. Multiple input/output devices 1550 may be present incomputer system 1500 or may be distributed on various nodes of computersystem 1500. In some embodiments, similar input/output devices may beseparate from computer system 1500 and may interact with one or morenodes of computer system 1500 through a wired or wireless connection,such as over network interface 1540.

As shown in FIG. 15, memory 1520 may include program instructions 1525,configured to implement certain embodiments described herein, and datastorage 1535, comprising various data accessible by program instructions1525. In an embodiment, program instructions 1525 may include softwareelements of embodiments illustrated in the above figures. For example,program instructions 1525 may be implemented in various embodimentsusing any desired programming language, scripting language, orcombination of programming languages and/or scripting languages (e.g.,C, C++, C#, JAVA®, JAVASCRIPT®, PERL®, etc.). Data storage 1535 mayinclude data that may be used in these embodiments (e.g., recordedcommunications, profiles for different modes of operations, etc.). Inother embodiments, other or different software elements and data may beincluded.

A person of ordinary skill in the art will appreciate that computersystem 1500 is merely illustrative and is not intended to limit thescope of the disclosure described herein. In particular, the computersystem and devices may include any combination of hardware or softwarethat can perform the indicated operations. In addition, the operationsperformed by the illustrated components may, in some embodiments, beperformed by fewer components or distributed across additionalcomponents. Similarly, in other embodiments, the operations of some ofthe illustrated components may not be provided and/or other additionaloperations may be available. Accordingly, systems and methods describedherein may be implemented or executed with other computer systemconfigurations.

It will be understood that various operations discussed herein may beexecuted simultaneously and/or sequentially. It will be furtherunderstood that each operation may be performed in any order and may beperformed once or repetitiously. In various embodiments, the operationsdiscussed herein may represent sets of software routines, logicfunctions, and/or data structures that are configured to performspecified operations. Although certain operations may be shown asdistinct logical blocks, in some embodiments at least some of theseoperations may be combined into fewer blocks. Conversely, any given oneof the blocks shown herein may be implemented such that its operationsmay be divided among two or more logical blocks. Moreover, althoughshown with a particular configuration, in other embodiments thesevarious modules may be rearranged in other suitable ways.

Many of the operations described herein may be implemented in hardware,software, and/or firmware, and/or any combination thereof. Whenimplemented in software, code segments perform the necessary tasks oroperations. The program or code segments may be stored in aprocessor-readable, computer-readable, or machine-readable medium. Theprocessor-readable, computer-readable, or machine-readable medium mayinclude any device or medium that can store or transfer information.Examples of such a processor-readable medium include an electroniccircuit, a semiconductor memory device, a flash memory, a ROM, anerasable ROM (EROM), a floppy diskette, a compact disk, an optical disk,a hard disk, a fiber optic medium, etc. Software code segments may bestored in any volatile or non-volatile storage device, such as a harddrive, flash memory, solid state memory, optical disk, CD, DVD, computerprogram product, or other memory device, that provides tangiblecomputer-readable or machine-readable storage for a processor or amiddleware container service. In other embodiments, the memory may be avirtualization of several physical storage devices, wherein the physicalstorage devices are of the same or different kinds. The code segmentsmay be downloaded or transferred from storage to a processor orcontainer via an internal bus, another computer network, such as theInternet or an intranet, or via other wired or wireless networks.

Many modifications and other embodiments of the invention(s) will cometo mind to one skilled in the art to which the invention(s) pertainhaving the benefit of the teachings presented in the foregoingdescriptions, and the associated drawings. Therefore, it is to beunderstood that the invention(s) are not to be limited to the specificembodiments disclosed. Although specific terms are employed herein, theyare used in a generic and descriptive sense only and not for purposes oflimitation.

The invention claimed is:
 1. A power line communication (PLC) device comprising: a processor; and a memory coupled to the processor, the memory configured to store program instructions executable by the processor to cause the PLC device to: sequentially scan one or more time slots in each of a plurality of frequency bands; detect a packet transmitted by a second PLC device to the PLC device over one of the plurality of frequency bands; and synchronize additional packets received from the second PLC device across the plurality of frequency bands based, at least in part, upon the detected packet, wherein the additional packets are organized in a plurality of frames, each of the plurality of frames having been transmitted by the second PLC device to the PLC device over a respective one of the plurality of frequency bands, each frame having a plurality of time slots, and each time slot having a pair of beacon and bandscan packets, wherein each bandscan packet includes information indicating a frequency band distinct from any of the plurality of different frequency bands to be used by the second PLC device to communicate with the first PLC device in a direction from the second PLC device to the first PLC device.
 2. The PLC device of claim 1, wherein the processor includes a digital signal processor (DSP), an application specific integrated circuit (ASIC), a system-on-chip (SoC) circuit, a field-programmable gate array (FPGA), a microprocessor, or a microcontroller.
 3. The PLC device of claim 1, wherein the beacon packets are configured to inform the PLC device that the second PLC device is active.
 4. The PLC device of claim 3, wherein each bandscan packet includes a slot index indicating a position of its time slot within its respective frame and a band index indicating a corresponding one of the plurality of frequency bands.
 5. The PLC device of claim 1, the program instructions further executable by the processor to cause the PLC device to: calculate a channel quality metric for each of the plurality of frequency bands based, at least in part, upon respective ones of the plurality of frames.
 6. The PLC device of claim 5, wherein the channel quality metric includes at least one of a signal-to-noise ratio (SNR) or bit error rate (BER) calculation or estimation.
 7. The PLC device of claim 5, the program instructions further executable by the processor to cause the PLC device to: transmit one or more packets to the second PLC device, each of the one or more packets corresponding to one of the plurality of time slots, and each of one or more packets including an indication of the channel quality metric.
 8. The PLC device of claim 5, the program instructions further executable by the processor to cause the PLC device to: determine when to transmit the one or more packets to the second PLC device based upon at least one of: a round-robin or a carrier sense multiple access (CSMA) technique.
 9. A tangible non-transitory electronic storage medium having program instructions stored thereon that, upon execution by a processor within a first power line communication (PLC) modem, cause the first PLC modem to: in a first mode of operation, define a plurality of frames, each of the plurality of frames having a plurality of time slots; assemble a pair of beacon and bandscan packets within each of the plurality of time slots in each of the plurality of frames; and sequentially transmit each of the plurality of frames over a corresponding one of a first plurality of frequency bands to a second PLC modem over a power line; and in a second mode of operation, monitor one or more time slots in each of a second plurality of frequency bands over the power line, the second plurality of frequency bands different from the first plurality of frequency bands; detect a packet transmitted by the second PLC modem over one of the second plurality of frequency bands; synchronize receipt of additional packets transmitted by the second PLC modem across the second plurality of frequency bands based, at least in part, upon the detected packet; calculate a channel quality value for each of the second plurality of frequency bands based, at least in part, upon the additional packets; and select one or more of the second plurality of frequency bands for subsequent communications with the second PLC modem in a direction from the second PLC modem to the first PLC modem based, at least in part, upon the channel quality values.
 10. The tangible non-transitory electronic storage medium of claim 9, wherein the program instructions, upon execution by the processor, further cause the first PLC modem to: in the first mode of operation, receive a communication from the second PLC modem indicating one or more of the first plurality of frequency bands to be used in subsequent communications with the second PLC modem in a direction from the first PLC modem to the second PLC modem.
 11. The tangible non-transitor y electronic storage medium of claim 9, wherein the program instructions, upon execution by the processor, further cause the first PLC modem to: in the second mode of operation, communicate the selected one or more of the second plurality of frequency bands to the second PLC modem over each of the second plurality of frequency bands, the selected one or more of the second plurality of frequency bands to be used in subsequent communications with the PLC modem in a direction from the second PLC modem to the first PLC modem. 